Hydraulic brake



Sept. 22, 1936.

w. F. OUVER HYDRAULIC BRAKE Filed Dec. 5l, 1951 plied to mechanisms other than automobiles. I4 which is normally maintained full of iiuid.

y 30 as the description proceeds.

Patented sept. 22, 1936 l 2,054,862.

UNITED STATES PATENT ort-ICEl HYDRAULIC BRAKE Wallace F. oliver, Detroit, Mich., assignor to Hydraulic Brake Company, Detroit, Mich., a corporation of California Application December 31, 1931, Serial No. 584,038

s claims. (o1. 13e-152)` My invention relates to hydraulic brakes and hand or foot of the driver or by power means, as is described as applied to the hydraulic brake desired. y system of an automotive vehicle, although it is The master cylinder .9 contains a sealing equally adapted for use in hydraulic brakes apmember I3 provided with an annular chamber Ina hydraulic brake system it is of the utmost 'Ihe rear end of the sealing member I3 carries importance that the operating cylinders and a flexible gasket I5 which assists in excluding conduits be maintained solidly iilled with opair from the operating parts of the system. The erating liquid, and that no air be present in the forward end of the sealing member I3 is reduced, i

system. I have found that the best way to preas indicated vat I6, and is provided with a slot I1 10 vent air from getting into a hydraulic brake sysin which is located a pin I8 ailixed to the lugs I9 tem is to maintain the operating parts thereof of a piston 20. The pin I8 and slot I1 provide under super-atmospheric pressure. An object a lost motion connection between the piston and l of this invention is to accomplish this result. the sealing member, and this lost motion conl5 Another object is to provide mechanism for nection is lnormally maintained in the position 15 accomplishing this result which will be troubleshown in the drawing by the relatively strong free and inexpensive to manufacture and asspring 2I. semble. The forward face of the piston is provided Another object is toA provide mechanism which with a rubber cup washer 22 which, during the 20 will maintain the operating parts of the system forward stroke of the piston, seals against the 20 under super-atmospheric pressure but which cylinder wall but which, on the return stroke of will not interfere with the return of the brake the piston, can collapse to permit flow of iiuid shoes from operative to inoperative position. therepast. Tc facilitate such flow, the cup 22 is .Another object is to providel mechanism to provided with axial grooves in the periphery of 25 maintain the operating parts of the system units base portion and the piston -20 is provided 25 der super-atmospheric pressure without prowith small bores 23. The space in back of the viding any additional joints or connections at piston is maintained in communication with the which leakage might occur.y pipe 8 by means of the port 24. The forward Other objects and advantages will be apparent end of the sealing member I3 is likewise provided with openings 25 which maintain the 30 In the drawing, chamber I4 in communication with the reservoir Fig. 1 is a view showing the principal parts of by way of the port 24 and pipe 8. The lower a brake system, some of the parts'being in secend of the actuating lever I2 is pivoted at 26 tion for easier understanding; and to a piston rod 21, having a rounded forward end Fig. 2 is a view showing a detail of the conwhich normally rests in a socket formed in the 35 struction of the compression cylinder and is sealing member |3- Thele iS n0 Other' Connectaken on the line 2-2 of Fig. 1. tion between the piston rod 21 and the sealing Referring to the drawing, I have indicated at member I3 so that a pull on the lever I2 in a 5 a fluid reservoir of suitable size which may` backward directin Will Simply tend t0 Separate.

40 be mounted Ion the dash 6 of an automobile. the piston rod 21 from thesealng member I3 1ol This reservoir is maintained `under substantially and will not exert a backward force on the piston atmospheric pressure, either by providing the 20. A flexible boot 28 is preferably provided to upper end thereof with a small vent opening or exclude dust and.l dirt from ther cylinder mechapreferably by providing a valve mechanism 1 nism. v

similar to that disclosed in the application of A Spring 29 Serves t0 return the 111515011 20 120 45 Clarence V. Gardner, Serial No. 535,316, iiled the position shownin Fig. lof the drawing. This May 6, 1931, now Patent No. 1,889,857, dated spring 29 is weaker .than the spring 2|. One end December 6, 1932. The lower end of the reserof the spring 29 rests in a shallow metal cup lovoir 5 is connected to a pipe 8 leading to a comcated inside of the rubber cup washer .22 and pression cylinder 9 generally referred to in the the other end of the spring 29 rests against a 5o trade as a master cylinder. The mastercylin` valve mechanism 3D of the type claimed in the j" der 9 is mounted on a bracket I0 aillxed to the application oi Erwin F. Loweke, Serial No. frame of the vehicle and which herein is shown 337,122, filed February 2, 1929, now Patent No.. Aas. providing a pivot II for the brake operating 1,885,121, dated November 1, 1932.. This valve lever I2 which may be operated either by the mechanism need not be described in detail herein 55 and it will suftice to say that it includes a metal plate 3| having a central opening through which passes the liquid discharged from the compression cylinder. Beyond the plate 3| is a rubber cup 32 having openings in its bottom which are out of line with the central opening in the p1ate 3|. During the discharge of liquid from the compression cylinder the center of the cup 32 is flexed away from the plate 3| so that liquid may pass through the center opening of the plate, thence between the center of the plate and the center of the cup until it reaches .the openings in the center of the cup, `and thence through these openings. In order'for liquid to return to the compression cylinder, the pressure on the liquid must be suflicient to move cup 32 and plate 3| away from the end of the cylinder and against the tension of the spring 29, whereupon the liquid can flow around the edges of the cup 32 and plate 3|, and thence into the compression cylinder.

The discharge end of the compression cylinder is connected by conduits 33 with the motor cylinders which apply the brakes. These motor cylinders are most commonly located at the vehicle wheels and from such location are commonly referred to as wheel cylinders, although it is obvious that the brake members and motor cylinders may 4be associated with the propeller sha-ft of the vehicle or the axles at points spaced from the wheels, or may be placed at any other suitable location. vIn Fig. 1 I have indicated at 34 such motor cylinder mounted on the pan 35 attached to the part 36 which may be either the axle housing, diierential housing or torque tube of a vehicle. In order to accommodate the relative motion between the motor cylinder 34 and the compression cylinder 9, the conduit 33 is provided with a flexible portion, indicated at 31.

The motor cylinder 34 inclu-des opposed pistons 38, each of which is connected by a link 39 with a brake shoe 4|] pivoted at 4| to the pan 35. Guide means 42 are provided for the brake shoes 40, as are also the retracting'springs 43 which normally hold the brake shoes 40 against suitable stops 44. The springs 43 are relatively strong springs which require a greater fluid pressure to overcome them than is required to overcome the spring 2|.

Associated with the pistons 38 are flexible rubber cups 45 which are held againstthe faces of the pistons 38 by an interposed spring 46. The inner ends of the links 39 simply rest in sockets in the rear sides of the pistons 38 and when the stop members 44 are adjusted to position the shoes closer to the drum 41 to compensate for wear of the lining 48, the inner ends of the pins 39 simply move outwardly in their sockets without disturbing the pistons 38. This arrangement is advantageous as any outward pull on the pistons 38 might tend to draw air past the pistons and into the motor cylinder. Flexible caps 49 of rubber or other suitable material connect the ends of the motor cylinder 34 with the pins 39, and serve to exclude dirt and moisture from the motor cylinder.

In the normal condition of the brake system the parts are in the position shown in the draw-- ing, and the cylinders 9 and 34, conduits 8 and 33, chamber I4, and space between the sealing member I3 and piston 20, are completely lled with viluid. The reservoir is also partially lled with fluid under substantially atmospheric pressure. The pressure on the fluid in the compression cylinder is dependent upon the diierence in force exerted by the springs 2| and 29. In some instances it is unnecessary to use the valve mechanism 30, in which case the fluid in the conduits 33 and wheel cylinders 34 is under the same pressure as the fluid in the compression cylinder. In most instances, however, I nd it desirable to interpose the valve mechanism 39 between the discharge end of the compression cylinder and the conduits 33, in which case the iluid in the conduits 33 and motor cylinders 34 is maintainedat a pressure somewhat greater than the pressure maintained on the uid in the compression cylinder. This difference in pressure is equal to the pressure necessary to move the valve mechanism 39 against the tension of the spring 29.

The sizes of and forces exerted by the several springs would, of course, be different for diierent installations, and for diierent operating conditions it might be desirable to maintain different pressures in diierent parts of the system. By way of illustration, however, I give the following example which would be suitable for certain classes of vehicles operated under certain conditions.

In this example, the springs 43 are oi such size and strength that it requires a fluid pressure of approximately 50 pounds to move the brake shoes 40 against the tension of these springs. This means that when the brake is released, the springs43 will move the pistons 38 in the motor cylinder 34 inwardly with suicient force to create a pressure of slightly less than 50 pounds per square inch pressure on the iluid.

The spring 29 is made of such strength that a 5 pounds differential in fluid pressure must exist between the fluid on opposite sides of the valve mechanism 39 in order to move this valve mechanism away from its seat against the tension of the spring 29. The spring 2| is stronger than the spring 29 since the spring 2| must resist the thrust of the spring 29 and must have sufcient reserve to thrust the cup washer 22 across the port 5I and maintain the fluid in the compression cylinder under superatmospheric pres* sure. The spring 2| is made of suicient force to maintain a iluid pressure of 5 pounds per square inch in the compression cylinder. Since the fluid in the compression cylinder is maintained at 5 pounds per square inch above atmospheric pressure and the spring 29 and valve mechanism 3U maintain the iluid in the conduits and wheel cylinders at ve pounds above that existing in the compression cylinder, the fluid in the conduits and wheel cylinders is maintained at 10 pounds per square inch above atmospheric pressure.

When the actuating lever I2 is operated to apply the brakes, the sealing member I3 is moved toward the right, as shown in Fig, l. Since the fluid in the compression cylinder is already at a pressure which balances the tension of the spring 2|. the initial movement of the sealing member I3 will compress this spring and bring the sealing member into engagement with the piston 29, whereupon the piston will be moved toward the right, as viewed in Fig. l, and will discharge fluid from the compression cylinder into the conduits 33. This discharge of uid will actuate the motor cylinders 34 and cause the pistons thereof to move the brake shoes 49 into engagement with the brake drums 47. When the operator releases the lever I2, this lever is immediately returned to its initial position bya spring indicated at 50.

Since the pin 21 makes a separable connection with the sealing member I3, the return moveing. At the same time the springs 43 lare'tenclingto contract and return the pistons in the motor cylinders to retracted position, but before these pistons can resume their retracted position a quantity of uid must be discharged from each motor cylinder. The relatively long small bore conduits 33 and the valve mechanism 30 retard this return flow of iiuid from the motor cylinders so that the piston 20 is usually returned faster lthan the fluid is returned to the compression cylinder from the conduits and motor cylinders. This condition creates a vacuum in the compression cylinder which draws in additional fluid from the rear of the piston through the openings 23 therein and around the periphery of the cup washer 22 which partially collapses during the return movement of the piston. The valve mechanism 30 prevents this vacuum from extending to the conduits and motor cylinders.

When the piston 20 reaches the position shown in Fig. 1 of the drawing, it momentarily comes to rest. As the pistons of the motor cylinders, under thel inuence of the springs 43, continue to return fluid to the conduits 33, the valve mechanism 30 is forced from its seat and fluid flows therepast from the conduits 33 into the compression cylinder. During the return stroke of the piston 20 additional uid was drawn past the piston so that the compression cylinder, conduits 33, and motor cylinders, now contain more iiuid n than they can hold in a condition of rest. As the pistons of the motor cylinders continue to return, more and more fluid is returned to thecom- .pression cylinder and the piston 20 is forced back-'- wardly against the tension ofthe spring 2l until the cup washer 22 uncovers the port 5I through which the excess of liquid may return to the reservoir. This excess of liquid carries with it any air which may have leaked into the compression cylinder, conduits 33 or motor cylinders 34, and thus these parts of the system are maintained free of air.

As soon as the pistons of the motor cylinders have completely returned to normal position and the excess of iiuid has been returned to the reservoir, the valve mechanism 30 returns to its seat and the piston 20 is advanced under the influence of the spring 2l until the cup washer 22 closes the port 5I. Thereafter the fluid in the compression cylinder, conduits 33, and motor cylinders 34, is maintained under super-atmospheric pressure.

While I have illustrated and described a particular embodiment of my invention, itis to be understood that my invention is not limited to this particular embodiment but may be`incor-l porated in radically different structure and that the scope of my invention is limited solely by the following claims. j

I claim: 1. In a hydraulic brake system of the class described, a motor cylinder, brake means actuated thereby, return spring means for said brake means, a compression-cylinder, a'reservoir for supplying fluid to said compression cylinder, a conduit connecting said cylinders,y valve means interposed between said compression cylinder and said conduit, a spring acting on said valve means to maintain pressure in said conduit and motor cylinder, and means other than gravity to maintain said compression cylinder under a pressure greater than that existing in the reservoir.

2. In a hydraulic system of the class described,

'of the system maintained under superatmospheric pressure by said other means, land means for automatically returning excess fluid from said last-named part of the system to said reservoir.

3. A hydraulic brake system of the class described comprising `a motor cylinder, braking means actuated thereby, return spring mechanism for said braking means, a compression cylinder, a piston therein, a conduit connecting said cylinders, said cylinders and conduit being filled with fluid, valve means interposed between said compression cylinder and said conduit for maintaining the fluid in said conduit and motor cylinder under a greater pressure than the fluid in said compression cylinder, and a fluid reservoir constituting a source of supply for said cornpression cylinder, said piston constituting valve means interposed between said compression cylinder and said reservoir for maintaining the uid in said compression, cylinder under a pressure greater than that existing in said reservoir.

4. In a hydraulic brake system of the class described, the combination of brake elem'ents adapted to be moved into engagement with brake drums, a motor cylinder for moving said brake elements into engagement with said drums, a compression cylinder for creating pressure to actuate said motor cylinder, a piston in saidcompression cylinder, a conduit connecting said cylinders, a fluid reservoir forming a source of supply for said compression cylinder, said piston constituting valve means between said reservoir and said compression cylinder capable of maintaining a predetermined pressure in said cyl-.

inders and conduit, a second valve means between said compression cylinder and said conduit for increasing the pressure in said conduit and motor cylinder, and retractile means for said brake elements capable of returning fluid tol said reservoir past said valves.

5. In a hydraulic brake system-of the class described, the combination of a compression cylinder for discharging fiuid under pressure, arconduit connected to said compressor, brake mechanism associated with said conduit and operable responsive to compression and decompression of the uid therein, afluid reservoir under substantially atmospheric pressure, resilient means indei pendent of said reservoir for maintaining `the uid in said compressor, conduit and mechanism under super-atmospheric pressure, means for automatically withdrawing an excess quantity of uid from said reservoir and forcing it into that part of the system maintained under super-atmospheric pressure by said resilient means, and means for automatically returning excess'uid from said lastnamedpart of the system to said reservoir.

6. In brake mechanism of the class described, a compression cylinder having one end exposed to atmosphere, a piston therein, a flexible packing member for said piston, said piston having openings therethrough, a sealing member engaging said piston, said sealing member serving to exclude atmospheric air from said cylinder and to prevent leakage of fluid therefrom, a lost motion connection between said sealing member and said piston, said sealing member and said piston being of the same diameter, a spring acting to separate said sealing member and said piston, actuating mechanism engaging said sealing member, and a fluid reservoir communicating with said sealing member and the rear of said piston.

'7. In a hydraulic system of the class described, a motor cylinder, means operated thereby, return springs for said means, a compression cylinder having one end exposed to atmosphere, a conduit connecting said cylinders, a piston in said compression cylinder, a sealing member adjacent said piston vand of the same diameter as said piston, said sealing member serving to exclude atmospheric air from said compression cylinder and to prevent leakage of fluid therefrom, said piston and sealing member providing a space therebetween, means for varying said space, and a reservoir communicating with said space.

8. I'n brake mechanism of the class described, the combination of a motor cylinder, brake means operated thereby, return springs for said brake means, a compression cylinder having one end exposed to atmosphere, a conduit connecting said cylinders, a piston in said compression cylinder, a. sealing member in rear of said piston and movable with respect thereto, said sealingmember providing an annular fluid chamber and serving to exclude atmospheric air from said cylinder and to prevent leakage of uid therefrom, said piston provided with openings to permit ow of fluid therepast on the return stroke, a fluid reservoir, connections from said reservoir to said chamber and the rear of said piston, a port for connecting said reservoir with the cylinder in front of said piston, and means normally maintaining said piston in a position closing said port.

WALLACE F. OLIVER. 

